Traditional printing devices rely on a mechanically operated carriage to transport a print head in a linear direction as other mechanics advance a medium in a direction orthogonal to the print head linear direction. As the print head moves over the medium, an image may be deposited to the medium. Portable printers have been developed through technologies that reduce the size of the operating mechanics. However, the principles of providing relative movement between the print head and medium remain the same as traditional printing devices. Accordingly, these mechanics may limit the reduction of size of the printer, the material that may be used as the medium, and the manner that images are printed.
Handheld devices are emerging that allow an operator to manipulate the handheld device over a medium to scan or print an image. However, such handheld devices are challenged by the unpredictable and nonlinear movement of the device by the operator. For example, the variations of operator movement, including rotation of the device, make it difficult to determine the precise location of a print head or scanning sensor relative to the medium. This type of positioning error may diminish the quality of scanned or printed images.
Current sensor schemes for positioning and navigation of a handheld device over a medium may have position accuracy errors that stem from inadequate sensor accuracy or inherent sensor error associated with a distance traveled by the sensor during a navigation process. Such sensor schemes may operate on a medium such that only relative positioning to a previous point on the medium is obtainable as opposed to absolute positioning relative to the medium. A handheld printing device using such sensor schemes may lose position information when lifted away from the medium reducing the ease of printing. Moreover, a printing device using such sensor schemes may not be able to determine a relative position to the medium when returned to the medium after being lifted away.
Positioning errors may have deleterious effects on print quality. For example, variations of print density may be discernible in printed images made by emerging handheld printing devices. Errors may be attributed to variability of sensor timing and other inaccuracies associated with positioning. For example, predictive processes that may be used to determine positioning may have positioning errors caused by delays in obtaining information from sensors. Extrapolated positions computed from inaccurate position data may further exacerbate such errors. Print quality may be further diminished when all printing material is deposited in a single pass as opposed to multiple passes